My early research focused mainly on the geology of the Appalachian Piedmont and the kinetics of metamorphic processes. During the last decade, my interests shifted first to questions of how the solid earth interacts with the biosphere, the atmosphere, and the hydrosphere—how Earth functions as a system—and then to the questions of sustainability—how to live indefinitely within the limits imposed by the Earth system.

The problem of sustainability has at least two dimensions: the ecological and the cultural. The ecological dimension reflects our need to understand all that we can about the limits imposed on society by the Earth system. The cultural dimension emerges from the realization that resources and the capacity of the Earth system to absorb waste products are limited. We must therefore think deeply about fundamental issues of equity that emerge from the tension between the desire to meet human needs and the necessity of preserving ecological system, the need to reconcile consumption patterns established in the developed world with legitimate aspirations of the international community, and the obligation to preserve meaningful options for future generations. Those questions must be worked out in the context of ethics and religious thought. Consequently, the issue of sustainability sits squarely at the confluence of two great streams of human thought, science and religious reflection. Exploring that confluence is one of the major intellectual challenges facing the academy today, a challenge which goes to the heart of the questions of who we are and how we are to live. 

An essay, "On Common Ground" appeared in Johns Hopkins Magazine, February, 2000, adapted from a talk given to the Johns Hopkins Center For A Livable Future, December 1999, in which I argued that science and religion are each essential parts of our humanity, and any hope for a sustainable future must be shaped by both.